Equivalent Static Method for CFST Arch Bridges Under Hanger Cable Fracture

Literature Overview

This paper, published in the China Civil Engineering Journal (Vol. 56, No. 6, 2023, pp. 63-74) by Chen Kangming, Wu Qingxiong, Luo Jianping, and Wang Huanwei from Fuzhou University, presents a methodological advancement in the analysis of medium and lower through concrete-filled steel tube (CFST) arch bridges under hanger cable fracture conditions. The research was supported by the National Key R&D Program of China (2017YFE0130300), the National Natural Science Foundation of China (Grants 52078137 and 51678154), and the Fujian Provincial Natural Science Foundation Distinguished Young Scholar Project (2019J06009). The study combines experimental testing, finite element modelling, and parametric analysis to develop an equivalent static calculation method that accounts for the dynamic effects of hanger cable fracture.

Research Methodology and Experimental Setup

The research methodology involved three key components: experimental testing, finite element modelling, and parametric analysis. A large-scale scaled model of a 20-meter span lower through CFST arch bridge was designed and fabricated, incorporating a novel electromagnetic cable fracture trigger device capable of achieving instantaneous hanger cable fracture within 0.1 seconds. This trigger device represents a significant innovation in experimental methodology, as it enables the simulation of realistic cable fracture conditions that are difficult to achieve with conventional testing methods.

The following table summarises the key components of the research methodology:

Dynamic Response Findings

The study revealed several important findings regarding the dynamic response of CFST arch bridges under hanger cable fracture. First, the hanger cable fracture has a significantly greater effect on the displacement and stress of the longitudinal girder than on the arch rib, which is a counterintuitive finding that has important implications for the design of cable-stayed and arch bridge systems.

Second, the fracture of longer hanger cables produces greater displacement and stress effects on both the longitudinal girder and the arch rib compared to shorter cables. Third, the fracture of the second-shortest hanger cable produces the greatest effect on the cable force of adjacent hangers, which is critical for understanding the progressive failure mechanism of hanger cable systems.

The following table summarises the recommended dynamic coefficients for the equivalent static calculation method:

Engineering Practice Implications

The development of an equivalent static calculation method for CFST arch bridges under hanger cable fracture is a significant practical advancement because it simplifies the analysis process while maintaining accuracy. Engineers can now use conventional static analysis software to evaluate the structural response of arch bridges to cable fracture events by applying appropriate dynamic coefficients, rather than performing complex dynamic finite element analyses for every design scenario.

However, several practical considerations must be addressed. First, the dynamic coefficients recommended in this study are based on a specific set of standard bridge configurations and may not be directly applicable to all bridge geometries and loading conditions. Engineers should exercise caution when extrapolating these coefficients to non-standard configurations and should consider conducting additional dynamic analysis for critical or unique bridge designs.

Second, the study focuses on a single cable fracture event, but real-world scenarios may involve multiple cable failures, either simultaneously or sequentially. The interaction between multiple cable fractures and the resulting progressive failure mechanisms require further research to provide engineers with comprehensive design guidance for cable redundancy and progressive collapse prevention.

Third, the long-term fatigue performance of the bridge components under repeated cable fracture events, such as those caused by construction errors or maintenance activities, has not been addressed. Engineers should consider incorporating fatigue assessment into the design process to ensure the long-term integrity of the bridge structure.

Key Questions and Reflections

Several important questions arise from this research that warrant further investigation. First, the study does not address the effect of cable fracture on the overall stability of the bridge under combined loading conditions, such as traffic loads, wind loads, and seismic loads. The interaction between cable fracture dynamics and other load combinations is critical for the design of robust bridge systems.

Second, the study focuses on medium and lower through CFST arch bridges, but the findings may not be directly applicable to upper through CFST arch bridges or other bridge types, such as cable-stayed bridges or suspension bridges. The dynamic response characteristics of different bridge types under cable fracture conditions may vary significantly, and additional research is needed to extend the equivalent static method to a wider range of bridge configurations.

Third, the study does not address the effect of material nonlinearity on the dynamic response of the bridge under cable fracture conditions. The steel tubes and concrete cores of CFST arch ribs may exhibit significant nonlinear behaviour under the high stress levels induced by cable fracture, and the linear dynamic coefficients recommended in the study may not fully capture this nonlinearity.

Study Insights and Implications

This research makes a significant contribution to the field of bridge engineering by providing a practical and validated equivalent static calculation method for the analysis of CFST arch bridges under hanger cable fracture conditions. The recommended dynamic coefficients of 1.8 for longitudinal girders and 1.7-1.8 for hanger cables offer engineers a straightforward tool for evaluating the structural response of arch bridges to cable fracture events, thereby enhancing the robustness and resilience of bridge designs.

For the steel pipe and welding industry, this study highlights the importance of ensuring the structural integrity and fatigue resistance of CFST arch ribs and hanger cable anchorages, as these components are critical to the overall robustness of the bridge system under cable fracture conditions. Engineers should pay particular attention to the welding quality of CFST arch rib joints and hanger cable anchorages, as these welded connections are potential weak points in the structural system.

In conclusion, this study provides a valuable methodological advancement in the analysis of CFST arch bridges under hanger cable fracture, and the recommended dynamic coefficients and equivalent static calculation method offer engineers a practical and efficient tool for enhancing the robustness and resilience of arch bridge designs in the face of cable failure events.